volume, and the importance of the line, and then determine the track structure for each grade. In Japan, railway lines are classified into 5 grades.
3 Countermeasures for Track Improvement I Modernization
3.1 Strengthening of Track Structures
The three factors of train load damaging force, track structural strength and labor for track maintenance work must be well-balanced. A track structure that is too resistant to deterioration results in increased capital outlay. However, if the structure is too weak for damage by train load, repair costs rise. The ideal structure is one in which the sum of both costs are kept to a minimum. Therefore, increases in transport volume, higher speeds and other changes call for improvements to current track structure.
An effective and economical method of strengthening track structure should be chosen, looking at one or several of the following.
(1) Rails
Heavy rails have efficient cost performance for increasing the strength of track structure.
However, if we were to make only the rails heavy, the rail axial tension or compression force brought about by temperature changes would increase, leading to other problems such as buckling of the track or excess gap at rail joints. Tracks should be strengthened maintaining the ideal balance for all the constituent elements.
Head-hardened rails are an effective measure against rail wear on sharp curves, and are also employed to reduce maintenance costs.
(2) Sleepers
Increasing the number of sleepers is one way to strengthen track structure. Along curves this is effective against both track deterioration and lateral force and is therefore recommended.
Recently, diminishing forest resources have caused the price of wooden sleepers to shoot up, making them by no means a reasonably-priced material. Steel sleepers have drawn interest as recyclable material, but most sleepers these days are made of concrete. Concrete sleepers (mainly prestressed concrete) have a long service life, are heavy and stable, and are highly resistant to track deterioration. Other advantages include the fact that they are well-matched to continuous welded rails, the use of which is spreading, as will be described later.
